The mononuclear phagocytic system is part of the immune system. It consists of the phagocytic cells that are primarily involved in phagocytosis and antigen processing and presentation. Thus, the system is a part of both humoral and cell-mediated immunity. Apart from immune functions, the system is also involved in the formation of plasma proteins, new erythrocytes and leukocytes, and bile pigments, the storage of excess iron (e.g. as ferritin and as hemosiderin), the removal of old RBCs and WBCs by phagocytosis, and the clearance of heparin with the help of the enzyme heparinase.2